1. Technical Field
The present invention relates to wireless communications, and more particularly, to operation of a relay station in a wireless communication system.
2. Related Art
Wireless communication systems are widely spread to provide various types of communication services. A wireless communication system may be a multiple access system capable of supporting communication with multiple users by sharing available system resources (i.e., bandwidth, transmit power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
The wireless communication system typically includes a base station (BS) providing a service to a cell that is a specific region located around the BS. Conventionally, a mobile station (MS) can communicate with the BS when the MS is located within a cell. However, when an obstacle such as a building or the like exists or when the MS is at the cell edge, the MS may not be able to communicate with the BS or communication quality between the MS and the BS may degrade.
Several schemes have been proposed to extend the service coverage of the BS and to improve service quality at the cell edge. In one of the schemes, a relay station (RS) is employed in the wireless communication system. The RS relays communication between the BS and the MS (or between two MSs or between a MS/BS and another RS). Here, the RS delivers data between a BS and a MS through two-hop or multi-hop links other than a single direct link. The RS can extend the service coverage of the BS and can improve cell edge performance. In addition, the RS can also improve cell throughput.
Some RSs use a time division duplex (TDD) wireless communication system such as mobile WiMAX (e.g., the Institute of Electrical and Electronics Engineers (IEEE) 802.16j/m). Since a downlink phase and an uplink phase are periodically alternated in the TDD wireless communication system, a guard time is required between the two phases. In a TDD-mode relay, a downlink and uplink traffic ratio can be adaptively regulated by relatively changing the number of orthogonal frequency division multiplexing (OFDM) symbols assigned to each of downlink and uplink.
Some RSs use a frequency division duplex (FDD) wireless communication system. Examples of FDD wireless communication systems include an FDD-based 3rd generation project partnership (GPP) long term evolution (LTE) system, a mobile WiMAX system supporting FDD, etc., which is for exemplary purposes only. Notably, an FDD-mode relay does not require a guard time between downlink and uplink, and interference between downlink transmission and uplink transmission less occurs in the FDD-mode relay than the TDD-mode relay.
In the conventional TDD wireless communication system, the TDD-mode relay is made possible by adding an RS having a transceiver of a legacy TDD station to the conventional system. This is because the TDD wireless communication system allows each station (i.e., BS, MS, and RS) to use all frequency bands at a time assigned for downlink or uplink. However, in the conventional FDD wireless communication system, it is difficult to operate normally when a system consisting of the conventional BS and the conventional MS is added to an RS having a transceiver compatible with the legacy TDD station or the legacy FDD station. This is because a full frequency band is divided into a downlink frequency hand and an uplink frequency band in the FDD wireless communication system. Therefore, there is a need for a new station for the FDD wireless communication system, a structure of the system, and a method of effectively using radio resources in the FDD wireless communication system.